Tribological assessment of a flexible carbon-fibre-reinforced poly(ether-ether-ketone) acetabular cup articulating against an alumina femoral head

New material combinations have been introduced as the bearing surfaces of hip prostheses in an attempt to prolong their life by overcoming the problems of failure due to wear-particle-induced osteolysis. This will hopefully reduce the need for revision surgery. The study detailed here used a hip simulator to assess the volumetric wear rates of large-diameter carbon-fibre-reinforced pitch-based poly(ether-ether-ketone) (CFR-PEEK) acetabular cups articulating against alumina femoral heads. The joints were tested for 25 x 10(6) cycles. Friction tests were also performed on these joints to determine the lubrication regime under which they operate. The average volumetric wear rate of the CFR-PEEK acetabular component of 54 mm diameter was 1.16 mm(3)/10(6) cycles, compared with 38.6 mm(3)/10(6) cycles for an ultra-high-molecular-weight polyethylene acetabular component of 28 mm diameter worn against a ceramic head. This extremely low wear rate was sustained over 25 x 10(6) cycles (the equivalent of up to approximately 25 years in vivo). The frictional studies showed that the joints worked under the mixed-boundary lubrication regime. The low wear produced by these joints showed that this novel joint couple offers low wear rates and therefore may be an alternative material choice for the reduction of osteolysis.     

Estimating parameters of the synchronous twofold-stochastic flow of events

Consideration was given to estimation of the parameters of the synchronous twofold-stochastic flow of events which makes up a mathematical model of the information flow of demands circulating in the queuing systems and networks. Two variants were studied. For the first variant, the problem of optimal estimation of the parameters of a synchronous flow of events with a finite arbitrary number of states was solved. The second variant differs in that the event flow operates in the environment where part of events is lost during the so-called dead time. Consideration was given to a synchronous flow with two states. The problem of estimating the length of the dead time in the conditions of continued dead time was solved. The results of numerical estimation based on the simulation model of the synchronous flow were presented for both variants.     

Mechanism responsible for the cooling of air heated by a strong shock wave

The problem of the cooling of a spherical volume of air after departure of a shock wave in air of normal density is studied numerically. Based on the results obtained, a conclusion is made that no radiative cooling wave exists in a real atmosphere.Academic Scientific Complex A. V. Luikov Heat and Mass Transfer Institute of the Academy of Sciences of Belarus, Minsk, Belarus. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 66, No. 2, pp. 155–158, February, 1994     

Embrittlement of Armco iron by indium at high temperatures

We determined the relative elongation () and ultimate strength (_u) of hollow Armco iron specimens and Armco iron specimens filled with indium at high temperatures in a vacuum. It was shown that indium embrittles Armco iron in the temperature range 850–950°C. The lowest values of were obtained at a temperature of 925°C, where a small amount of the -phase is observed in the structure of strained specimens. The high-temperature liquid metal embrittlement of Armco iron is caused by an indiummelt-induced decrease in the flow stress, which localizes strains in the -phase and initiates its premature cracking. On the basis of metallographic investigations, we made the conclusion that corrosion is not responsible for the high-temperature liquid metal embrittlement of Armco iron.Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv. Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 29, No. 6, pp. 41–45, November–December, 1993.     

Application of the digital signal processing methodology (DSPM) for the design of time integration formulae

Although the existence of a close relationship between the areas of digital processing and time integration methodology has been established long ago, only recently a systematic application of the concepts and methods of the first area to the second has been attempted. The resulting Digital Signal Processing Methodology is applied in this paper to demostrate that time integration methods can be designed, displaying advanced performance in the computational analysis of large complex systems, with respect to accuracy, spurious oscillations damping, overshooting and asymptotic behavior for singular cases.     

Solvent effect on ageing of silica gels

The structure of silica gels derived from tetraethoxysilane (TEOS) with molar compositions of TEOSH₂OHNO₃=1100.4 and then aged in various solvents, was studied. The effect of various solvents having different physical properties on the gel structure, as well as the relationship between the solvent properties and the dried gel structure, were investigated. The density, surface area and pore-size distribution were measured. The results of the pore structure and SEM showed the aged gels to have a slit-shaped micropore, narrow pore-size distribution, and homogeneous microstructure. The density, surface area, pore size and pore volume of dried gels changed as the gels were subjected to ageing in various solvents. The surface area could be related to the polarity parameter of the ageing solvent.     

Filter elements of the wound type

NTF Inprokom (St. Petersburg). Translated from Khimicheskie Volokna, No. 5, pp. 46–48, September–October, 1993.     

Standing waves of gaseous chemical reactions in inert porous media

Standing waves of gaseous, exothermic, chemical reactions in inert porous media are investigated in the two-temperature and one-temperature approximations. A semiinfinite reaction zone method is developed to solve the problem analytically. It is shown that the wave solutions obtained by this method form a large set. Traditional solutions with strong heat transfer at the end of the wave make up but a small fraction of this set.LENIIKhIMMASh, St. Petersburg 193167. Translated from Fizika Goreniya i Vzryva, Vol. 30, No. 4, pp. 11–20, July–August, 1994.